UPDATE - Voters cast ballots in Japan upper house election

UPDATES WITH TURNOUT DATA

TOKYO (AA) – Japanese citizens flocked to polling stations Sunday to vote in an upper house election as the ruling coalition seeks to match its commanding majority in the more powerful lower chamber.

With half of the 242 seats in the House of Councillors up for grabs, Prime Minister Abe's Liberal Democratic Party (LDP) and its allies are pursuing a majority that would be seen as an endorsement of his signature economic strategy, known as Abenomics.

The main suspense, however, is whether or not they will win a two-thirds majority that would allow the cabinet to propose changes in the American-written constitution that was adopted after World War II.

Local news agency Kyodo reported that government data showed that voter turnout stood at 22.5 percent as of 2 p.m. (0500GMT), with polling stations set to close at 8 p.m.

During the 18-day official campaigning period that wrapped up Saturday, opposition parties had warned against granting Abe the power to pursue constitutional reform, while the ruling parties pledged to work toward sustainable economic growth amid international uncertainty.

Half of Japan’s upper house -- comprised of 242 members, elected to fixed, six-year terms -- is up for election every three years. Electors vote twice: once for the proportional list and once for prefectural districts.

Sunday’s polls are notable for two more reasons other than the pursuit of a majority.

It is the first election to be held since the voting age was lowered from 20 to18.

It is also the first test case of the alliance for convenience between the main opposition DP and the Japan Communist Party --who have agreed to coordinate their election campaigns so that they don’t split the opposition vote.

The results are expected to be clear by early Monday.